1. Field of the Invention
The invention relates to a wheel supporting device that includes a hub unit to which a wheel is fitted and a joint coupled to the hub unit.
2. Description of Related Art
For example, Japanese Patent Application Publication No. 2009-78675 (JP 2009-78675 A) describes a wheel supporting device that includes a hub unit and a constant velocity joint. In this wheel supporting device, in order to allow transmission of torque between the hub unit and the constant velocity joint, a first spline is formed on an axially inner end face of a rotary ring of the hub unit, and a second spline that is in mesh with the first spline is formed on an axially outer end face of an outer ring of the constant velocity joint.
Each of the first and second splines has a plurality of projections that extend radially. The hub unit and the constant velocity joint are brought into contact with each other in the axial direction to mesh these splines with each other. Then, the hub unit and the constant velocity joint are fastened to each other, with a bolt, in the axial direction. In this way, the hub unit and the constant velocity joint are assembled together.
At the time of the above-described assembly, alignment between the first spline of the hub unit and the second spline of the constant velocity joint in the circumferential direction is not particularly performed. Therefore, as shown in FIG. 10, top lands 103 of the projections 102 of the first spline 101 may contact, in the axial direction, with top lands 114 of the projections 113 of the second spline 112. In this state, the hub unit and the constant velocity joint may possibly be fastened to each other with a bolt. When torque acts between the hub unit and the constant velocity joint in this state, a slip occurs between the projections 102 and the projections 113, and the projections 102 of the spline 101 fall down the gaps between the projections 113 of the spline 112. As a result, the splines 101 and 112 are in mesh with each other. However, in this case, clearances between the projections 102 and 113 in the circumferential direction are large. As a result, poor meshing occurs. That is, for example, a play that causes noise occurs or transmission of torque is interrupted.
Therefore, according to JP 2009-78675 A, an axial through-hole formed in the rotary ring (hub spindle) of the hub unit has a small-diameter hole portion that provides a slight clearance between the inner periphery of the rotary ring and a shaft portion of the bolt, and tapered hole portions into which the distal end of the shaft portion of the bolt is inserted and along which the distal end of the shaft portion is guided.
With the configuration described in JP 2009-78675 A, alignment between the huh unit and the constant velocity joint is facilitated, and the possibility that poor meshing between the splines will occur is slightly reduced. However, the diameter of the through-hole of the rotary ring is reduced along the overall length due to the formation of the small-diameter hole portion and the tapered hole portions. Therefore, the wall thickness (the size in the radial direction) of the rotary ring increases, resulting in an increase in the weight of the rotary ring.